Acrylamide is widely utilized as a raw material for polymers used for many applications such as aggregating agents, thickening agents, oil recovery agents, paper power enhancing agents in the papermaking industry and thickening agents for papermaking. Examples of methods for industrially producing acrylamide include: a sulfuric acid hydrolysis method comprising the step of heating acrylonitrile with sulfuric acid and water to obtain amidosulfate; a method in which acrylonitrile is hydrated in the presence of a catalyst (e.g., metallic copper, copper oxide and copper salt); and a method in which acrylonitrile is hydrated using a microbial cell having nitrile hydratase activity.
Among such methods, a method using a microbial cell having nitrile hydratase activity is remarkably effective as a method for industrially producing acrylamide because reaction conditions are mild with almost no by-product and a very simple process can be employed. Further, using the method, a high-quality polyacrylamide having a significantly-high molecular weight with no insoluble impurity can be produced (Patent Document 1). For this reason, the method is the dominant method for producing acrylamide.
Like many other unsaturated monomers, acrylamide is easily polymerized by light and heat, and in addition, has a characteristic that it is significantly easily polymerized when brought into contact with the surface of iron. For this reason, in the production process of acrylamide, in order to stabilize acrylamide produced, the production is conducted under the conditions of light interception and low temperature (about 20° C.) and in the state in which contact with iron surface is avoided as much as possible. Further, addition of a stabilizer for suppressing polymerization of acrylamide is widely used.
Examples of stabilizers include 8-hydroxyquinoline, cupferron iron salt (Patent Document 2), thiourea, ammonium thiocyanate, nitrobenzol (Patent Document 3), ferron (Patent Document 4), furildioxime (Patent Document 5), a chrome-cyanogen complex (Patent Document 6), p-nitrosodiphenylhydroxylamine (Patent Document 7), 2,6-di-t-butyl-3-dimethylamino-4-methylphenol (Patent Document 8), 4-aminoantipyrine, oxalic acid, hydroxylamine sulfate (Patent Document 9), a mixture of manganese with a chelate compound (Patent Document 10), water-soluble monocarboxylic acid salt having at least two carbon atoms (Patent Document 11), a sulfur-containing compound and a mildly acidic salt (Patent Document 12).
As a method for preventing polymerization without using any stabilizer, a method for preventing polymerization of acrylamide which is prone to occur on the wall surface of the gas phase portion in an apparatus for use in the acrylamide production process by coating the wall surface of the gas phase portion with a synthetic resin-based material is shown (Patent Document 13).
Further, as a method for preventing polymerization of acrylamide which is prone to occur in a fluid accumulation portion in an apparatus for use in the acrylamide production process, the following methods are shown: a method in which a portion which may be in contact with a fluid accumulation portion is made of a resin (Patent Document 14); and a method for forcibly removing a process fluid accumulated in a fluid accumulation portion from the portion (Patent Document 15). Examples of such fluid accumulation portions include the inside of a pipe for sampling branched from the main pipe, a valve or the like. It is impossible to remove such a fluid accumulation portion by design choice. When a polymerized product is generated at a fluid accumulation portion, it may block the flow in a pipe, or the generated polymer may remove from the fluid accumulation portion and get mixed in with a process fluid, which may cause polymerization in a tank or the like downstream.    [Patent Document 1] Japanese Laid-Open Patent Publication No. H09-118704    [Patent Document 2] Japanese Publication for Opposition No. S39-23548    [Patent Document 3] Japanese Publication for Opposition No. S30-10109    [Patent Document 4] Japanese Publication for Opposition No. S40-7171    [Patent Document 5] Japanese Publication for Opposition No. S40-7172    [Patent Document 6] Japanese Publication for Opposition No. S41-1773    [Patent Document 7] Japanese Publication for Opposition No. S45-111284    [Patent Document 8] Japanese Publication for Opposition No. S47-4043    [Patent Document 9] Japanese Publication for Opposition No. S47-28766    [Patent Document 10] Japanese Publication for Opposition No. S48-3818    [Patent Document 11] Japanese Patent No. 2548051    [Patent Document 12] Japanese Laid-Open Patent Publication No. 2003-206268    [Patent Document 13] Japanese Publication for Opposition No. S49-16845    [Patent Document 14] Japanese Laid-Open Patent Publication No. 2003-221374    [Patent Document 15] Japanese Laid-Open Patent Publication No. 2003-221373